The present invention relates generally to manufacturing processes, and, more specifically, to shot peening of workpieces.
Metal components or parts are typically manufactured in multiple steps to achieve the final size, configuration, and surface finish thereof. Metal components may be cast in complex three dimensional (3D) configurations, with and without subsequent precision machining of various surfaces thereof.
A gas turbine engine includes many complex 3D parts cast and machined for use in various components thereof. Turbine rotor blades include an airfoil extending outwardly from a supporting platform and dovetail. The dovetail is configured with axial lobes or tangs for mounting each blade in corresponding dovetail slots in the perimeter of a supporting rotor disk.
During operation, energy is extracted from hot combustion gases that flow past the turbine rotor blades which in turn rotate the supporting rotor disk for powering a compressor in a typical configuration. The blades are subject to centrifugal loads during operation, which loads are carried radially inwardly through the supporting dovetails into the perimeter of the rotor disk.
The turbine blades are typically formed of high strength superalloy material having enhanced strength at the elevated temperatures typically found in the turbine. To further enhance the strength of the turbine rotor blades the various surfaces of the dovetails may be shot peened in one of the last manufacturing steps producing the blades.
Shot peening is a mature process in which metal shot is discharged in stream of pressurized air over the surface of a metal workpiece to plastically deform the surface layer thereof and introduce residual compressive stress therein. The residual compressive stress reduces the stresses experienced in the component during operation, such as in the rotating environment of the gas turbine engine.
Since the shot peening process is effected at the end of the manufacturing cycle for the typical component, corresponding care must be used in the process to avoid damaging the component or incompletely shot peening the intended surface thereof. Uniform shot peening of the entire turbine blade dovetail, for example, will ensure maximum strength of the blade during operation and a correspondingly long service life.
However, shot peening adds to the time and cost of manufacture of components, such as the turbine blades, and in the typical gas turbine engine a multitude of turbine blades are found and must be suitably manufactured at competitive cost.
In one conventional shot peening apparatus enjoying many years of successful commercial service in the United States, individual turbine blades are mounted upside down in corresponding supporting cans which expose upwardly the corresponding dovetail while protecting the turbine airfoil inside the can.
Eight blades in corresponding cans may be mounted to the perimeter of a supporting turntable inside a fully enclosed cabinet for performing shot peening of the blade dovetails. Each can is indexed into position next to a gang or set of shot peening nozzles mounted from a common support rod. The individual nozzles in the set are manually aligned with a single dovetail for aiming the shot stream at a common target point thereon.
During operation, the cabinet is closed, and the support rod for the nozzles oscillates vertically for discharging the shot stream simultaneously from the set of nozzles over the surface area of the blade dovetail as it rotates with the can on the common turntable.
In less than a minute per blade, the entire dovetail may be suitably shot peened over its full exposed surface notwithstanding the serpentine configuration of the serrations or dovetail lobes thereon. The use of accurately aligned multiple shotpeen nozzles ensures accurate shot peening of the dovetail as it rotates during the process while the nozzles oscillate vertically.
However, each of the multiple nozzles requires corresponding initial alignment relative to the corresponding blade workpiece supported in the can, which alignment is typically done manually by an operator and therefore extends the setup time of the process.
Furthermore, two sets of shotpeen nozzles may be mounted inside the cabinet from corresponding supporting rods for permitting the simultaneous shot peening of two blade dovetails in their corresponding supporting cans.
Each of these multiple shotpeen nozzles must be independently aligned with the corresponding workpiece. And, each of the nozzles in each set must also be aligned relative to each other for ensuring the coincidence of the separate shot streams therefrom at a common target point on the workpiece.
The blade workpieces are typically shot peened in large batches following the initial alignment of the nozzles in the cabinet. The blades are simply inserted into the corresponding supporting cans for shot peening thereof and replaced by subsequent turbine blades until the full batch of blades has been shot peened. Prior to the next batch of blades requiring shot peening, the alignment of the shotpeen nozzles is measured in a conventional manner using Almen strips, with the multiple nozzles being realigned if required.
Accordingly, it is desired to provide an improved shotpeen nozzle in a multi-nozzle apparatus for shot peening workpieces with improved alignment of the nozzles.